Radiation conduit for radiation source

Abstract

A radiation source includes a fuel supply configured to deliver fuel to a plasma emission location for vaporization by a laser beam to form a plasma, and a collector configured to collect EUV radiation emitted by the plasma and direct the EUV radiation towards an intermediate focus. The collector includes a diffraction grating configured to diffract infrared radiation emitted by the plasma. The radiation source includes a radiation conduit located in between the collector and the intermediate focus. The radiation conduit includes an entrance aperture connected by an inwardly tapering body to an exit aperture. The radiation conduit includes an inner portion and an outer portion, the inner portion being closer to the intermediate focus than the outer portion. The inner portion is configured to reflect incident diffracted infrared radiation towards the outer portion.

What is claimed is: 
     
       1. A radiation source comprising:
 a fuel supply configured to deliver fuel to a plasma emission location for vaporization by a laser beam to form a plasma; 
 a collector configured to collect EUV radiation emitted by the plasma and direct the EUV radiation towards an intermediate focus, the collector comprising a diffraction grating configured to diffract infrared radiation emitted by the plasma; and 
 a radiation conduit located in between the collector and the intermediate focus, the radiation conduit comprising an entrance aperture connected by an inwardly tapering body to an exit aperture, the radiation conduit comprising an inner portion and an outer portion, the inner portion being closer to the intermediate focus than the outer portion, wherein the inner portion is configured to reflect incident diffracted infrared radiation towards the outer portion. 
 
     
     
       2. The radiation source of  claim 1 , wherein the inner portion comprises a reflective structure and the outer portion comprises an absorptive structure. 
     
     
       3. The radiation source of  claim 1 , wherein the inner portion comprises a plurality of faces oriented to reflect incident diffracted infrared radiation towards the outer portion. 
     
     
       4. The radiation source of  claim 3 , wherein the plurality of faces are oriented to reflect first order incident diffracted infrared radiation towards the outer portion. 
     
     
       5. The radiation source of  claim 3 , wherein at least some of the plurality of faces subtend an angle of less than 70° relative to an angle of taper of the radiation conduit. 
     
     
       6. The radiation source of  claim 4 , wherein at least some of the plurality of faces subtend an angle of 61° or less relative to an angle of taper of the radiation conduit. 
     
     
       7. The radiation source of  claim 3 , wherein the plurality of faces extend around the interior of the radiation conduit in a direction substantially transverse to an optical axis of the radiation source. 
     
     
       8. The radiation source of  claim 1 , wherein the outer portion comprises a plurality of ridges angled away from the intermediate focus. 
     
     
       9. The radiation source of  claim 1 , wherein the outer portion comprises a first absorptive structure and a second absorptive structure. 
     
     
       10. The radiation source of  claim 9 , wherein the second absorptive structure comprises a plurality of faces configured to receive infrared radiation reflected from the inner portion of the radiation conduit, and to reflect that infrared radiation across the radiation conduit. 
     
     
       11. The radiation source of  claim 9 , wherein the second absorptive structure has a saw-tooth form. 
     
     
       12. The radiation source of  claim 11 , wherein the second absorptive structure includes faces substantially perpendicular to one another and oriented to retro-reflect infrared radiation that has traveled across the radiation conduit. 
     
     
       13. The radiation source of  claim 9 , wherein the first absorptive structure comprises a plurality of ridges angled away from the intermediate focus.